1. Field of the Invention
The present invention relates to a lens-fitted photo film unit. More particularly, the present invention relates to a lens-fitted photo film unit of which a lid openable for removing a photo film cassette is improved for convenience of treating the cassette.
2. Description Related to the Prior Art
A lens-fitted photo film unit contains a cassette, into which photo film is wound each time an exposure is taken. There is a bottom lid, which is disposed under the cassette to cover a bottom of a cassette containing chamber, and opened to remove the cassette with the photo film from the lens-fitted photo film unit. The cassette has a spool, which has a top end engaged with a shaft portion under a photo film winding wheel.
It requires external operation in a photo laboratory to remove the cassette from the lens-fitted photo film unit even when the bottom lid is opened. This is because the top end of the spool is engaged with the shaft portion of the photo film winding wheel. An operator of the photo laboratory shakes down the lens-fitted photo film unit in the axial direction of the spool for the purpose of detachment of the spool. It is likely that the cassette, when shaken in sufficiently quick motion, is thrown out, striking a wall or floor, and damaged irrecoverably.
A new type of photo film cassette is suggested by U.S. Pat. Nos. 4,834,306 and 4,832,275 and commonly assigned U.S. Pat. Nos. 5,271,577 and 5,407,146 (both corresponding to JP-A 3-37645). A photo film inclusive of a leader is pre-contained in a cassette shell. Rotation of a spool causes the photo film to advance to the outside of the cassette shell. There is another suggestion in that a cassette shutter is incorporated in a photo film passage port in openable fashion without using a light-trapping fabric, so as to reduce frictional resistance to advancement of the photo film.
It is conceived that a lens-fitted photo film unit, for use with the photo film cassette having the cassette shutter, is provided with a cassette shutter drive mechanism in the cassette containing chamber. When the cassette is loaded, the cassette shutter is open. The engagement of the cassette shutter with the drive mechanism makes it more difficult to remove the photo film cassette from the cassette containing chamber. This is because both the spool and the cassette shutter must be disengaged before removal.